That *is* the MikesXS aftermarket advancer unit, which has a history.
You could mark/grind a line directly above the advancer's stop pin,
View attachment 151114
With the right cylinder at TDC compression, that scribe line should be pointing straight up.
The aftermarket slotted disc is a fairly rough casting, compared to the OEM machined disc.
View attachment 151115
Want to see if the disc's indexing slot is straight between the big notches.
If it was flipped over, backside to front, and timing tested, any timing change would indicate that its slot is off-center. It may even correct your timing...